1. Field of the Invention
The present invention relates to a solid-state light shutter array element usable for a writing head of an optical printer.
2. Description of the Prior Art
Recently, computers have progressed to promote automation in every technical field, and the field of information processing technique has been remarkably improved. A printer for use as the information output apparatus is a component playing a very important role. Various types of printers have actively been developed, among which the optical printer, a kind of non-impact printer, has been the most prominent one. A device comprising a light shutter formed in an array using the electro-optical effect is used as the writing device for the optical printer.
At present, a light shutter array element which employs an electro-optical material is well known. The element comprises a transparent substrate of lanthanum modified lead zirconate titanate (PLZT) having a composition of La/Zr/Ti=9/65/35 having very large Kerr effect, a plurality of opposing electrodes formed on the substrate, and polarizing plates disposed at both sides of the substrate.
The principle of operation of the light shutter is that an electric voltage is applied between the opposite electrodes formed on the PLZT substrate to cause birefringence thereon, thereby varying the polarization condition of an incident light. The light beam shutter using the PLZT substrate is characterized in that the response speed is fast, which has hitherto been fully studied and also examined in the light shutter array.
A light shutter array using a PLZT substrate was reported in "PLZT LINEAR ARRAY PAGE COMPOSER" by George R. Laguna, Ferro-electrics Vol. 10 (1976), pp. 35-38, and Elektronic Industrie Vol. 6 (1980). p. 26.
Such PLZT light shutter array, however, has a large problem in that the permeability will vary after a long period of use of the shutter array. The reason for this is that the electrostriction phenomenon of the PLZT material causes mechanical stress on the PLZT substrate. Especially, the stress is caused by variation in the electrostriction caused by abrupt variation in the electric field distribution at the end portion of each electrode. An improvement for solving the above problem has been disclosed in Japanese Laid-Open Patent Application No. 50-130464. This improvement, however, is very difficult to achieve and is not applicable to a light shutter array having many light shutter portions.